This invention relates to a system for acquiring, processing, storing, transmitting and displaying data relative to the physiological condition of a critically ill patient in a hospital.
The first generation prior art of patient monitoring apparatus comprised sensors attached to the patient to provide analog signals such as the electrocardiogram (ECG), blood pressure, temperature and others. Detected analog signals were amplified and processed, and displayed essentially as analog signals on devices such as oscilloscopes, calibrated meters and strip chart recorders. Initially, these apparatus were located at the bedside of the patient. In more advanced installations a number of bedside units were connected to a central station which had analog display devices. This permitted medical personnel at the central station to monitor the dynamic wave forms of several patients simultaneously. Whenever a certain monitored parameter from a certain patient exceeded a preset limit, and audio alarm notified medical personnel of the problem. Thus, the first generation of patient monitoring apparatus was primarily a collection of analog units, each performing a single function.
The first generation patient monitoring systems had several disadvantages. Amont them is that data could not be stored in the best form. Only dynamic wave forms could be stored and reviewed later when some alarm condition occurred. Data transmission was limited, and a separate analog line was required for each wave form and each derived parameter which was to be transmitted from any bedside to a central station. Any communication from the central station to the bedside station required separate analog lines from those used to transmit physiological data from the bedside to the central station. Further disadvantages were that the amount of display hardware needed to monitor the patient became excessive, distracting and was more difficult for medical personnel to monitor.
A second generation of patient monitoring apparatus was designed to overcome some of the disadvantages in data processing, storage and displaying inherent in the first generation of patient monitoring systems. The second generation system added a central computer to the previously existing bedside and central station units. The system was thus endowed with the capability for deriving more complex, physiological parameters by way of computer programs, storing derived parameters for later review by medical personnel, and generating graphs and/or hard copy of stored data.
Among the disadvantages of the second generation systems were that they had the same limitations on data transmission between the bedside and central station units as did the initial systems. An additional set of analog lines were required to transmit each distinct wave form and each distinct derived parameter to the central processor. A separate set of digital lines were required from the central processor to the digital display. The second generation systems also lacked a capability for convenient expansion. Additional amplifiers, processors, display devices and/or modifications of existing display devices were required to expand the system.
A significant improvement in patient monitoring systems, was described in U.S. Pat. No. 3,925,762 to Heitlinger, et al and assigned to the same assignee as the present invention. This prior art system utilized a central processor in the central station and could accomodate up to four bedside stations. A distinctive feature of the above system was the use of a set of digital data busses and digital interfaces for two-way transmission of all data between all units in the system. The system was inherently computer compatible because all of the data was communicated in digital format. All data sources converted information into digital words before transmission and all receivers read digital words. The data sources or senders throughout the system had binary counters which began counting simultaneously upon occurrence of a synchronizing pulse which was applied to all of them at the same time so that they all counted in synchronism. Generated data words each had a time slot which was identified by a count number with respect to a count initiating sync pulse. The words were gated into the data busses synchronously and repetitively. The receivers had counters which were all synchronized by the same sync pulse as were the senders so that they counted correspondingly. Any receiver which was designated to receive a particular word counted the same number as did the sender when the data was gated onto the bus and the receiver was controlled by a logic system, as was the sender, to open its gates simultaneously to enter and store the data during its short appearance on the bus.
The above system provided some distinct features and advanced the patient monitoring art. However, the system was limited to four bedside stations for each central station, and the system was extremely complex and expensive.